Molded-one piece articles are used, for example, in forming printed circuit boards. In many instances, two separate molding steps are used to form two portions of the article. Two-shot molding is a means of producing devices having two portions, such as molded interconnect devices (including printed circuit boards), from a combination of two injection molded polymers. The process is also used for producing two-colored molded plastic articles and for combining hard and soft plastics in one molded part.
Molded interconnect devices (MIDs) are used in a variety of industries and applications, including for example, sensors, switches, connectors, instrument panels and controllers. MIDs typically have at least one electrical trace created, usually by plating of a conductive metal, on a molded plastic structure.
One method of creating MIDs involves molding part of a structure in one mold, using a first plastic material and then placing the structure, which has been created in the first mold, in a second mold and then molding the second portion of the part with a second plastic material. The two plastic materials are chosen so that a conductive material can be plated on one of the plastic materials and not on the other plastic material. The conductive material, which can be plated on the platable plastic, becomes a conductive trace or other feature. The conductive trace carries data signals, control signals or power to and from components of the application. A photo-imaging process may be used in which a mask is applied and the coated mask is selectively exposed to ultraviolet (UV) light to selectively harden the mask to non-circuit areas. The unexposed mask is chemically removed, revealing a circuit pattern. The pattern is then plated with copper or other metal to achieve a desired circuit performance.
More recent developments in plastic injection molding have allowed for molding MIDs in a single shot. For example, a structure can be produced from a single photosensitive non-conductive material, such as a thermoplastic doped with an organic metal complex. An interconnect path is then written on the molded structure, for example, by using a laser which breaks the metal atoms from the organic ligands, allowing the metal atoms to act as nuclei for copper plating. The laser beam produces a local activation of the substrate surface, by which the desired circuit layout is made. Thereafter, immersion in a metal plating bath, which is typically copper, allows plating of metal onto areas etched by the laser beam, allowing traces or other features to be created in those areas. This process is known as a Laser Direct Structure (LDS) process and provides designers with a simpler one-shot molding process that allows for creation of circuitry after the molding process is complete, without a tooling change, and provides the capability to produce a component with a higher resolution and smaller footprint.
The LDS process provides a straightforward three-step process that includes: (1) creating the substrate using a standard injection molding process utilizing a laser-activatable non-conductive substrate material that contains a metal compound; (2) activating the non-conductive material with a laser, such that the metal compound is broken down into its associated metal which acts as a seed layer for subsequent electroless plating thereon; and (3) electroless plating of the activated portions of the non-conductive substrate.
The laser activation step creates a micro-etched surface that provides excellent bonding characteristics for the electroless metal that is subsequently applied thereto. The electroless metal may comprise copper or copper alloy although other electroless metals are also usable.
A problem associated with substrates formed by the LDS process, is that extraneous plating can occur, particularly on rough areas of the substrate or on areas of the substrate that have been mechanically damaged.
Based thereon, it is an object of the present invention to provide a method of treating molded interconnect devices to avoid undesirable extraneous plating.